The present invention relates to a method of controlling the speed of a vehicle, in particular as a function of a vehicle traveling ahead in the same lane.
It is known, for example, from German Patent No.197 22 947, that the vehicle traveling ahead can also be detected taking into consideration the course of the road, e.g., in curves, basically via signals produced by a sensor, e.g., a radar sensor.
In addition, it is known from German Patent Application No. 42 42 700 that a radar sensor for detecting a vehicle traveling ahead can be mounted on a vehicle. This radar sensor is, e.g., a component of an ACC (adaptive cruise control) vehicle comfort system, in which information regarding the distance and relative speed of the vehicle with respect to other vehicles and to the road conditions is processed on an ongoing basis.
For example, an FMCW (frequency modulated continuous wave) radar, having both the transmission technology with an antenna system for generating the radar beams and a receiver with analysis electronics, is mounted in the outside front area of the vehicle in a manner known from German Patent Application No. 195 30 065. A multibeam method according to German Patent Application No. 195 30 065 also allows the lateral position of objects, e.g., vehicles in a curve, to be determined.
The aforementioned speed controlling in an ACC system takes place so that the travel speed is adjusted to slower vehicles traveling ahead if these are measured by the radar distance sensor with limited detection range and are located in the area of the vehicle""s expected path. Traveling along a curve represents a particularly critical situation for the response of the system, since, on the one hand, the predefined desired speed may be too high for traveling along a curve and, on the other hand, the area detected by the radar sensor is limited in the curve, and therefore vehicles traveling ahead are detected with a delay, which may result in critical closeness.
It is also known, for example, from the journal article xe2x80x9cAbstandsregelung mit Radarxe2x80x9d [Distance control using radar], F. Ackermann, Spektrum der Wissenschaft, Ed. 6/80, pp. 24-34, that the lane or the path can be predicted using the vehicle""s own sensors already provided for other purposes. For example, the yaw rate detected using an appropriate sensor, i.e., the angular velocity of the vehicle about its vertical axis, or the transverse acceleration acting on the ACC vehicle can be evaluated in order to limit the speed. In this way, however, a curve is not detected until the vehicle is in the curve, so that it is too late to meaningfully predict the vehicle""s path. In particular, speed control relative to vehicles traveling on adjacent lanes must also be prevented in this case at the beginning of a curve.
A method of controlling the speed of a vehicle in which at least one vehicle traveling ahead in the same lane within the detection range of a radar is detected using a radar sensor and in which the transverse acceleration in the vehicle to be controlled is detected is advantageously refined according to the present invention.
Acceleration or a change in acceleration is limited in a simple manner in the vehicle to be controlled if, in addition to or instead of a transverse acceleration, information on the vehicle reaching the limits of the radar detection range and/or on the vehicle traveling ahead leaving the radar detection range is evaluated when no change of lanes takes place. The present invention advantageously ensures reliable operation of the above-mentioned ACC system in curves. This is possible by combining the aforementioned different approaches, which prevent uncomfortable or undesired acceleration before or in curves.
Thus, according to the present invention, the acceleration or change in acceleration in a curve in the presence of a transverse acceleration not yet approaching the acceleration limit in the ACC vehicle is limited as a function of the limited radar sight range. The radar sight range results from the geometric relationships between the course of the road and the radar detection range of the radar sensor on the ACC vehicle. One criterion for determining the acceleration limitation is the time period (TRange) until the ACC vehicle has reached the lateral limit (xcex1Range) of the radar detection range. From this point on, objects farther away, traveling in their own lanes, can no longer be detected by the radar sensor due to the course of the road, which may result in dangerous closeness to vehicles traveling ahead.
It is furthermore particularly advantageous if the acceleration limitation becomes stronger as the radar detection range becomes shorter measured in units of time.
When operating the ACC system, the problem may also arise that when or before the ACC vehicle enters a curve, the vehicle traveling ahead, which is already in the curve, is lost as the target object because it has left the radar detection range, while the ACC vehicle has not yet reached the actual curve area. This kind of target object loss can therefore be detected, when no change of lanes takes place, if the target object is on the path of the ACC vehicle until the target object is lost and is not assigned to an adjacent lane.
Also in this case, either the acceleration or the change in acceleration of the ACC vehicle can be limited after this type of target object loss has been recognized. The response time is of the order of magnitude of the actual time window for a target object loss and can be selected to be proportional to the latter.